Firefox recently switched to a 64-bit version that does not support NPAPI plugins, rendering the Unity Web Player unsupported. Current Firefox users are not automatically updated to this version, but anyone downloading for the first time will have the 64-bit version downloaded by default. Below are the steps to replace it with the 32-bit version that supports the Unity Web Player:
- Go to firefox.com and click on the “System & Languages” button.
- In the search bar, type “English” to narrow the results.
- Under the “Windows” column (NOT the “Windows 64-bit” column), find the link that says “Download” for English (US).
- The Firefox Setup file will download. Once it’s done downloading, run the file to install the proper version.